Physique

Nombre total de résultats : 278
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Physical investigations on perovskite LaMnO3-δ sprayed thin films for spintronic applications

A.Boukhachem. A.Ziouche. M.BenAmor. .O.Kamoun. M.Zergoug, .H.Maghraoui-Meherzi, .A.Yumak, K.Boubaker, M.Amlouk  (2016)
Publication

Oxygen deficient LaMnO3 thin films were successfully grown on glass substrate by spray pyrolysis at 460 °C. XRD studies show oxygen vacancies corresponding to the orthorhombic La4Mn4O11 with (040) preferential orientation. Optical properties were investigated through optical band gap and Urbach energy. The dispersion of the refractive index was discussed in terms of both Cauchy and Wemple & Di-domenico models. Raman spectroscopy shows the band positions corresponding to LaMnO3 with a shift related to oxygen deficiency. Electrical properties were quantified using impedance spectroscopy technique within frequency range of 5 Hz–13 MHz at various temperatures. Both the DC conductivity and relaxation frequency were thermally activated with activation energy around 0.9 eV. Also, AC conductivity was investigated through Jonscher law. Finally, magnetic measurements at room temperature using vibrating sample magnetometer (VSM) technique show ferromagnetic behavior of these ternary sprayed thin films. Voir les détails

Mots clés : Thin films, Magnetic Properties, Raman spectroscopy, Impedance spectroscopy, X-ray diffraction, Dielectric properties

Microstructure and Magnetic Properties of NiP Alloys

S. Alleg, A. Boussaha, W. Tebib, M. Zergoug, J. J. Su?ol  (2016)
Publication

Ni-P alloys were prepared by electrodeposition on a copper substrate at different plating conditions (applied potential and deposition time). The morphology, composition, microstructure, structure, and magnetic properties of the films were investigated by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and vibrating sample magnetometry, respectively. The phosphorous content is about 8.6–12.2 at.%. The deposits exhibit either a nanocomposite structure where Ni(P)–1 and Ni(P)–2 solid solutions are embedded into an amorphous matrix, or a mixture of Ni2P phosphide and Ni(P)–1 and Ni(P)–2 solid solutions. The coercivity and magnetization are plating condition dependent. All samples exhibit a soft magnetic character with coercivity lower than 58 Oe. The squareness ratio Mr/Ms values that are in the range 0.019–0.123 correspond to a multidomain (<0.1) for all samples except sample B (−1.15 V, 10 min) which falls into a pseudo-single domain (Mr/Ms = 0.123). Voir les détails

Mots clés : Electrodeposition Ni-P alloys Microstructure Magnetic properties X-ray diffraction

Microstructural Study of Thin Films CuFe Obtained by Thermal Evaporation of Nanostructured Milled Powder

H. Mechri, Ahmed HADDAD, M. Zergoug, Mohammed AZZAZ  (2017)
Publication

Commercial copper and iron powders were used as starting materials. These powders were mechanically alloyed to obtain Cu(100-x) Fex supersaturated mixture. The milling duration was chosen in such a way as to obtain a nanostructured mixture and to form a supersaturated solid solution of CuFe; the powder mixture was used to deposit CuFe on a glass substrate. The elaboration of our films has been carried out using thermal evaporation process (physical vapor deposition) under 1 × 10-6 mbar vacuum from an electrically heated tungsten boat, using the supersaturated solid solution Cu(100-x) Fex powder obtained by mechanical alloying. The films deposition has been done on glass substrates. In this study, we present the composition effect on the structural and magnetic proprieties of Cu(100-x) Fex powder and thin films. The chemical composition, structural and magnetic proprieties of milled powders and thin films were examined by SEM, TEM, XRD, XRF and VSM. Voir les détails

Mots clés : CuFe Solid Solution, DRX, MET, microstructure, thin film, VSM

RF magnetron sputtering deposition of NiO/Ni bilayer and approach of the Magnetic behavior using the Preisach model

A. Bendjerad, S. Boukhtache, A. Benhaya, A. Lahmar, M. Zergoug, D. Luneau  (2017)
Publication

Bilayer of nickel and nickel oxide were deposited on glass substrates using RF magnetron sputtering technique. The magnetic properties of the prepared thin films were carried out at room temperature in both parallel and perpendicular magnetic field to the sample. The Preisach model was applied to provide a mathematical model of the magnetic hysteresis loop in the case of parallel geometry, along the easy axis of the bi-layer NiO / Ni. Good agreement was obtained between the theoretical and experimental results. Voir les détails

Mots clés : Ni/NiO bilayer;, Magnetic properties;, Preisach Model

Spatio-temporal aspects of the domain propagation in a spin-crossover lattice with defect

R. Traichea, H. Oubouchoua, M. Zergoug, K. Boukheddaden  (2017)
Publication

the collective spatiotemporal dynamics of the metastable high-spin state (HS) upon relaxation towards the low-spin (LS) is investigated using an electro-elastic model which includes the change of the spin states and the lattice volume at the transition. The present work focusses on the case of a lattice in which is embedded a structural defect in the center, represented here by a hole with a fixed size. The simulations are made on a 2D rectangular-shaped and compared to those of an ideal system. To account for the volume change, we set the distances between the sites as spin-dependent which requires the use of Monte Carlo simulations on spin states and atomic positions to solve the present problem. It is found that the presence of the defect affects the dynamics of the spin-crossover transformations which starts stochastically from a corner of the lattice, then propagates in the first stage along the width (shortest distance to the surface), before to proceed via a second longitudinal regime whose velocity slows down significantly at the vicinity of the defect, which plays the role of a pining center. After a while, the interface leaves the defect, and accelerates when it approaches the lattice's border. We have also investigated the spatial dependence of the displacement field, from which we derived the distribution of the divergence and rotational of the displacement field, which directly connects to the trace of the strain tensor and to shear strains respectively. Valuable information on the relaxation process of the elastic field are derived and discussed in direct relation with the presence of the defect. Voir les détails

Mots clés : Spin Crossover, Phase transition;, Interface propagation;, Spatiotemporal effects, elasticity

Degradation of plastic pipe surfaces in contact with an aggressive acidic environment

W. Ghabeche, L. Alimi, K. Chaoui  (2015)
Publication

olyethylene (PE) pipes transporting water are vulnerable to aggressive agents which are able to diffuse through buried plasticpipes causing oxidative degradation. The latter may occur as a result of a spontaneous chemical reaction with atmospheric oxygen or as an induced oxidizing reaction with disinfectant agents (i.e. chlorine or hypochlorous acid ions) which are commonly added to municipal water supplies for public health reasons. Basically, PE pipes surfaces undergo undesired oxidation reactionswhenever they are in contact with adverse external environments and/or when conveying fluids which tend to modify internal pipe wall structure. In this work, the effects of distilled water and diluted hydrochloric acid at different concentrations on the external and internal surfaces of a high density polyethylene (HDPE-100) pipe are studied. The measured parameters are roughness and hardness in order to appreciate surface quality variances in as-received and degraded materials. Initially the outer surface is rougher than the inner’s one but in contact with distilled water, the external surface roughness increased by 6% although the internal face of the tube revealed a small decrease (<5%). When exposed to hydrochloric acid, pipe roughness (μm) showed a substantial increase as a function of increasing medium concentration. Crystallinity (χ in %) measurements confirmed the gap between outer (51.55%) and inner (61.31%) surfaces indicating that degradation has taken place at the structural level when HDPE was in contact with such aggressive agents. On the other hand, it is revealed that after exposure to oxidizing environments, crystallinity dropped by approximately one third when compared to as-received material; therefore reducing resistance to fracture and subsequently pipe lifetime. Voir les détails

Mots clés : polyethylene pipe; environment; distilled water; diluted hydrochloric acid; degradation; surface roughness; hardness; crystallinity.

First-principles prediction of the structural, elastic and mechanical properties of of hydrides Ba2RuH6

O. Boudrifa, A. Bouhemadou  (2017)
Article de conférence

We report a systematic study of the structural, elastic and mechanical properties of the ternary ruthenium-based hydrides Ba2RuH6 within first-principles approach. The elastic behavior of a cubic monocrystalline is characterized completely by ¶three elastic constant independent C11, C12 and C44.We note here the absence of any experimental or theoretical data on the single-crystal and polycrystalline elastic moduli and their related properties elastic constants for the studied materials to be compared with our findings. Voir les détails

Mots clés : Ruthenium-based hydrides; First-principles calculations; Elastic constants; Mechanical properties.

FIRST-PRINCIPALES STUDY OF THE STRUCTURAL, VIBRATIONA, PHONON AND THERMODYNAMIC PROPERTIES OF THE COMPLEX K2PtCl6STRUCTURE HYDRIDES Ca2OsH6.

O. Boudrifa, A. Bouhemadou  (2017)
Article de conférence

We have presented a full first-principles study of the structural, phonon and vibrational properties for Ca2OsH6 com-pound at the GGA-PBE level. The calculations are performed using the plane-wave pseudopotential method, density functional perturbation theory and the quasiharmonic approximation implemented in the CASTEP code. In particular, our theoretical lattice parameters obtained using the GGA-PBE to include the exchange-correlation functional are in good agreement with experiment. To our knowledge, there no experimental data or theoretical calculation for the study of frequency modes of NaCl structure of the studied hydrides for comparison. Voir les détails

Mots clés : ab initio, Hydrides, structural, phonon and vibrational properties.

First-principales study of the structural, vibrationa, phonon and thermodynamic properties of the complex K2PtCl6 structure hydrides Ca2OsH6

O. Boudrifa, A. Bouhemadou  (2017)
Article de conférence

We have presented a full first-principles study of the structural, phonon and vibrational properties for Ca2OsH6 com-pound at the GGA-PBE level. The calculations are performed using the plane-wave pseudopotential method, density functional perturbation theory and the quasiharmonic approximation implemented in the CASTEP code. In particular, our theoretical lattice parameters obtained using the GGA-PBE to include the exchange-correlation functional are in good agreement with experiment. To our knowledge, there no experimental data or theoretical calculation for the study of frequency modes of NaCl structure of the studied hydrides for comparison. Voir les détails

Mots clés : Hydrides, structural, phonon and vibrational properties, ab initio

Structural optical magnetic properties of Co doped -MoO3sprayedthin films.

A. Boukhachem, M. Mokhtari, N. Bznameur, A. Ziouche, M. Martinez, P. Petkova, M. Ghamnia, A. Cobo, M. Zergoug, M. Amlouk  (2017)
Publication

this works deals with the synthesis of Cobalt doped MoO3thin films which were grown on glass sub-strates by the spray pyrolysis at 460?C. First, X-ray diffraction analysis shows an orthorhombic structurerelated to -MoO3allotropic variety with (020) and (040) preferred orientations. The surface topogra-phy performed by atomic force microscopy (AFM) shows that the grain size varies from 150 to 280 nm.Second, optical parameters, such as optical band gap, Urbach energy, refractive index and dielectricconstants were studied in terms of Co content. This optical study shows a direct transition of all pre-pared thin films and normal dispersion of the refractive index showing both Cauchy and Wemple &Di-dominico variations. On the other hand, PL measurements show transition bands mainly in blue andgreen domains related to band-to-band transitions as well as to oxygen vacancy in all films. Finally, mag-netic measurements at room temperature using vibrating sample magnetometer (VSM) technique reveala ferromagnetic behavior of such doped films. Voir les détails

Mots clés : MoO3, Thin films, optical properties, Magnetic Properties, Spray pyrolysis